Process and apparatus for electrostatic separation of finely-divided discrete material



PROCESS AND APPARATUS FORYELECTROSTATIC SEPARATION OF PINELY DIVIDED DISCRETE MATERIAL.

G. R. BROWN.

APPLICATION FILED JAN. 7, 1920.

- Patented July 4, 1922.

4 SHEETS-SHEET I.

G. R; BROWN. PROCESS AND APPARATUS FOR ELECTROSTATIC SEPARATION OF FINELY DTVIDED DISCRETE MATERIAL v APPLICATTON FILED IAN- 7, 1920- 1,422,026. Patented July 4, 1922.

4 SHEETS-{SHEET 2.

I G. R. BROWN. PROCESS AND APPARATUS FOR ELECTROSTATIC SEPARATION OF FINELY DIVIDED DISCRETE MATERIAL,

APPLICATION FILED IAN- 7. 1920.

I Patented J uIy 4, 1922.

4 SHEETS-SHEET 3.

G. R. BROWN. PROCESS AND APPARATUS FOR ELECTROSTATIC SEPARATION OF FINELY DIVIDED DISCRETE MATERIAL.

' APPLICATION FILED JAN. 7, 1920.

4 SHEETS-SHEET 4.

Patented July 4, 1922.

v I: I 5%. .5 Q. -IIIHi ME I UNITED STATES PATENT OFFICE;

GEORGE RUDSTON BROWN, OF BONDI, NEAR SYDNEY, NEW SOUTH WALES, AUS- TRALIA, ASSIGNOR T0 ELECTROSTATIC SEPARATION COMPANY, LIMITED, 01' SYDNEY, NEW SOUTH WALES, AUSTRALIA, A COMPANY REGISTERED ACCORD- ING TO THE LAWS OF THE STATE OF NEW SOUTH WALES, IN THE COMMON- WEALTH OIE' AUSTRALIA.

PROCESS AND ArrAnA'rtis FOR ELECTROSTATIC SEITARATION c msonn'rn MATERIAL.

To all whom it may concern:

Be. it known that I, GEORGE 'RUDSTON BROWN, a subject of the King" of Great Britain, residing at Cremorne, Ewell Street, Bondi, near Sydney, in the State.

n the following is a specification.

This invention'relates to process and apparatus for the separation and or classification of particles possessing different. degrees of electrical conductivity of discrete metal- .liferous material such as metal bearing ores and other mlxtures whereln some mgredr cuts are susceptible to electrostatic influence while other ingredients are not so or are less susceptible and it has been specially devised in order to provide improved process and apparatus for such purposes which -will be eflicient in function.

Heretofore many proposals have been made to separate the particles of discrete materials of the class stated by means of electrostatic influence in a field of force be tween electrodes but these have not so far been successful as to justify toany appreciable extent the general adoption of any one of them, but that after many trialsand experiments present inventor has found by subjecting the material under treatment to the effect of heating and of mechanical force and or gravity in conjunction with electrostatic influence an efficient separation and or classification of particles of discrete material according to their electrical conductivity is obtained and he has applied this discovery in novel processand in novel ap paratus constituting "this invention.

In "this novel process for electrostatic separation of finely divided discrete mate rial such material is subjected to heat and centrifugal action whereby thoroughly dry and warm (preferably hot) it is caused to pass between electrodes whereby theparticles are electrically charged more or less according to their respective electrical con- Specification of Letters Patent.

' .i App1ic'ation filed January 7, 1920. Serial No. 349,975.

ductivity and so are repulsed and attracted until they reach respective zones wherefrom accordlng to the sustenation they derive from the electrostatic field of force'they may be collected in classes by ravity or otherwise. And the special merits of this new process are the thorough drying and warming or heating of the particles before thrusting them into an electrostatic fieldvof force the positioning of the effective electrostatic field of force within range of a revolving and another electrode or of a pair of revolving electrodes and feeding the particles thereto by means of centrifugal force and the collecting of the resultant classes of particles. I

O In the preferred construction of novel apparatus for electrostatic separation of finely divided discrete material a feeding hopper preferably revolving is secured on the top of the revolving hollow stem of a Patented July 4, 1922.

OF FINELY-DIVIDED centrifugal pan or fugal which is supported by its stem in bearings. in the machine frame, and which stem has through ports at the lower end thereof onto the floor of ,the fugal pan. This floor has heating de- \vices preferably electrical heating elements beneath it and the pan has preferably a cover plate fitted over its top extending almost to its rim. The fugal pan is electrically connected to earth and its cylindrical rim is electrically charged and acts asone electrode having spaced above it the other electrode in the form of a ring preferably revolvable supported by arms of insulating material aflixed to the fugal stem,

and the extent of gap or space between these electrodes may be adjustable if desired. A revolving dividing disc is positioned outwardly of the electrodes and may if desired form part (in conjunction with the pan rim) of the bottom electrode and has circular'channels or hoppers positioned inwardly and outwardly around it. A discharge lmpper preferably having curved vanes on its floor and revolvable oppositely tov the pan reaches from the dividing disc to a second hollowstem having similar bearings'tothose of the first fugal or in the V case of a battery of fugals the hollow stem reaches that of the next lower fugal. Needle sparking gaps are preferably arranged within this discharge hopper.

The integers or parts are mainly well encased but air ports are provided at the top and a suction device is connected to the lowermost part of the hollow of the fugal stem or stems.

When the combining of a plurality of the described fugals into a battery of same is desirable said fugals are preferably arranged one above the other and in such case a by-pass or cut out valve is arranged in each fugal stem operatable by a solenoid or an electric magnet.

But in order that these improvements in process and apparatus for electrostatic separation of finely divided discrete material may be readily applied in practice the novel process and the preferred construction of simple apparatus for carrying out said process will now be described with reference to the drawings accompanying and forming part of this complete specification.

Figure 1, is a partial sectional elevation of a complete machine having one fugal and one discharge hopper;

Fig. 2, is a plan view of the machine, and

Figs. 3 and 4, are horizontal sections on the lines 3-3 and 4-4, Fig. 1.

The apparatus has a suitable framing and easing hereinafter described surrounding a centrifugal pan 3 whose vertical hollow stem 4 integral therewith expands into a lower distributing chamber 5 provided with ports 6 leading into said pan 3. In or depending from the frame of the apparatus is a boss 7 to which is secured by means of nut 8 a liner 9 with a heel 1O (catching on the bottom of boss 7 and a foot flange 11 and this liner 9 supports the lower half 12 with a comple-' ment 13 (carried on a screwed bush 14) of the weight sustaining ball bearing of the fugal stem 4. A roller bearing 15 backing on liner 9 sits upon bush 14 and above it has distance rings 16 and 17 supporting a second roller bearing 18 while a nut 19 secures the whole of the bearings together and rigidly around the stem 4 while a dust cap 20 fits over the top. The three bearings are adapted to be oiled by a supply pipe 21 (from an oil pump say pump 22) passing through boss 7 under nut 8 and through liner 9 to the top of roller bearing 18.while the discharging oil is drawn from the oil Well 24 supported by stem 4 by the suction pipe 23 of same pump as 22. The stem 4 at top carries the feed hopper 25 having a driven gear wheel 26 in gear with pinion 27 of electrical motor 28. Inlet ports 29 are provided for entrance of air with the mineral to be treated to the fugal.

The pan 3 has sector slots 30 covered by annular plate 31 and a cylindrical outer wall terminating in rim 32. Electric hot-wire heating elements 33 of any well known construction are enclosed in suitable casings 34 and positioned under the plate 31 fastening on underside thereof. The top wall of the distributing chamber 5 carries the circular oil well 24. A ring 35 connects said oil well 24 to the pan cover 36 and so supports the latter. Within the ring 35 is a hood 37 with outlets at its top made by distance blocks 38 through which fastening studs pass to said ring 35. I

At the bottom of the distributing chamber 5 is a plate 39 secured to the top of acircular extension wall 40 with a flange 41 whereby it is secured to the bottom of the wall of said chamber 5. Said extension wall 40 provides space for a solenoid carrying frame which comprises a top circular spider piece 42 with vertical wall 43 through which it is secured to said extension wall 40 and a bottom spider flanged base 44 secured also to extension wall 40 through its flange 45. The solenoid coil 46 in a suitable protective casing is carried on the spider base 44 and its plunger 47 carries at its top the stem of a drop valve 48 having a seating on bottom plate 39.

Transformer coils 49 preferably in four pairs in suitable insulated cases are bolted or otherwise affixed to the extension wall 40 and each coil has a plurality of needle spark ing points 50 secured and protruding outwardly of the casing. One end of the sec ondary Winding'of each coil is earthed to the machine framing while the other end is elec trically connected to one set of needle points and so constitutes them the one side of two' sparking gaps.

The rim 32 of the pan 3 and if desired inward part of dividing disc73 forms one electrode of a field of force .of which the other electrode is ring 51 (preferably U- shaped) supported by radial arms 52 of insulating material whose inner, ends are secured in orifices in ring 53 affixed to oil well 24 while the outer ends by means of brackets 54 are secured by screws in webs 55 to the electrode ring 51.

Secured to a flange 56 of electrode ring 51 is a circular guard 57 having a flange 58 adapted to contact with a spring brush in a supply terminal 59 of one lead from a high tension source of electric supply such as a transformer with rectified current of or an influence machine of from 10,000 volts up-' wards but preferably from between 35000 to 1 300000 volts. The machine frame furnishing the return and completing the circuit.

The oil well 24 carries revolving insulated collecting ring 60 and this ring 60 contacts with a distributing spring brush on supply terminal 61 ofone lead from a source of electricity normally supplying say current of the usual power ranging from 200 to 600 volts the machine frame furnishing an earth return circuit. l

Outwardly of thepan 3 and below it is the discharge hopper 62 whose bottom flange 63 might be secured to a hollow stem 4 of a the floor of this hopper secured by flanges 66 to the extensionwall 40and to the wall of the pan 3. s The said discharge hopper 62 is revolved by a gear wheel 67 secured to flange 63 and meshing with pinion 68 of an electric motor 69 which alsodrivesan oil pump as 22 for lubricating the'bearings.

The stem 64 leadsinto stationary pipe 70- discharging say on to a conveyor belt or the like to waste or a dump and said pipe 70 has a pipe 71 in its side from a fan or other suction device (not shown). 7 7

To the rim of saidhopper 62 is bolted the T headed. ring 72 whose topmember is a dividing disc 73. Sector-hoppers 74.with

discharge pipes 75 adapted to take bags thereon are ositioned outwardly of the di- 3.which has aguard ring 76.

viding disc overlappingthe inner wallof the hopper 7 4.

From the collecting ring .60 independent- I insulated wiring is led respectively to the heating elements 33 to the transformer coils 1 49 and to the solenoid coil 46 with return leads earthed to the machine frame and with suitable switching for control purposes as well understood.

The framing and easing of this construction ofapparatus is made up of-the spider top 77 v from which the central bearing boss 7 depends and on this top-77 is a cover plate '78 on which is secured the. electric motor.

.28. The top 77 sits upon and secured to by screw bolts spaced pillars 79 surrounded by a casing 80 and positioned upon a slmilar spider frame77 upon alarge spider frame 81 (which might] be the top of the. next lower simila'r separating apparatus if a battery of such is used) and thisframe" 81 has supporting pillars 82 from base 83 and having surrounding casing providing a packing space 84 enclosedby plate 85 and top wall 86. The casing preferably {would tioned.

A greater recovery of ore and "a greater classification is assured by using aplurality of fugals'preferably positioned in tiers in" which case the gangue discharge hopper is have inspection 'doors conveniently posicarried on the stem of the next fugal or lower fugal and said gangue passes through fugal shown in the drawings and each have an independent power source and the mouths of each collecting hopper or bin would preferably lead into the one underneath.

In operation the current being switched on the motors 28 and 69 revolve the fugal and the discharge hopper 62 preferably in opposed direction. The material to be treated is thoroughly heated in contiguous ovens or in any well known manner and is fed into hopper 25 wherefromit passes down hollow fugal stem 4 into distributing chamber 5 and out through ports 6 and banking up within hood 37 enters pan 3 through the space under the said hood 37 as a narrow horizontal qircular stream, wkhilie {the air not passing under this ring 37 finds its way between distance pieces 38 into the passage between ring 35 and hood 37. The heat of the material and atmosphere is maintained, in the fugal pan 3 by means of the electric .heaters 33 in sector slots 30. The heated material thrown outwardly by the centrifugal force of the revolving pan 3 discharges in a very fine stream over the pan rim v32 contacting therewith and the particles of greater conductivity such as metallic bodies become electrically charged by their contact to a greater extent than particles of less conductivity (such as gan gue) and take the sign of the rim 32 and are elevated by the electrical force in the field between said rim 32 and the ring 51 and 'if electrified the di-V.

viding disc 73 (which negatives the force'of gravity) I to above the dividing disc 73 their.

movements being relative to their individual size and shapes and to the degree to which they have been electrically charged and or their retention of gravity. 6 v

The'electrica'lly charged particles are thus thrust through one zone of the electrostatic field of force between the rim and the electrode 51,- andthe particles of, comparative electrical conductivity which are influenced -to the desired degree are thrown into a sec- .ond "zone ofsaid field of force between the electrode 51 and the charged dividing disc 73, .and becoming elevated above the said" disc contacting or otherwise with the electrode 51 are trapped .and pass either directly to the hopper 74 or'are carried there by the centrifugal force of the revolution of.

the said disc'73, and drop into said hopper, and thence into pipes 75 to the floor below and preferably-into bags on said pipes 75.

The circular guard' 57' prevents any elevated particles which might under electrical III Ill

influence tend to travel inwardly from taking that course.

The gangue not being electrically infiuenced or influenced to the required extent is arrested by ring 72 and disc 73 and falls by gravity into discharge hopper 62 assisted by the draft or air current caused by suction in pipe 71. The dispersion of any dust arising is prevented by said draft as also by the electrical infiuence of the sparking in the needle gaps 50 of the transformer coils 49, The curved spider arms guide the fallen gangue on the fioor of hopper to the center of hopper 62 and it falls through hollow stem 64 and through di chargepipe onto a dump conveyor belt or the like or it a battery of fugals is used into the hollow stem thereof.

If it is desired as in the case of cutting out one or more of the fugals in a battery of same the material under treatment may be allowed to fall straight through the "fugal without entering the pan 3 by switching off the current from solenoid 46 when the plunger 47 will fall with the drop valve 48 and so open a free passage for the material ,t'rom distributing chamber 5 and through the orifices formed by the spider arms of the solenoid carrying frame into discharge hopper 62 or into a feeding hopper of a fugal below.

What I claim as my invention, and desire to secure by Letters Patent is 1. Process for electrostatic separation or" finely divided discrete material wherein the material dried and hot is centritugally cast against an electrode whereby its particles of comparative electrical conductivity become electrically charged and are thrust through one zone of an electrostatic field of force between said electrode and another electrode and to a second zone of said field material dried and hot is centrifugally cast against an electrode whereby its particles of comparative electrical conductivity are thrust through one-zone of an electrostatic field of force between said electrode and another electrode and to a second zone of said field of force where they are elevated more or less free of the force of gravity as they centrifugally travel through said second zone to a point of discharge, while particles of insuflicient electrical conductivity by arrest of centrifugal travel and by the force of gravity find another point of discharge,

substantially as described.

3. Process for electrostatic separation of finely divided discrete material wherein thoroughly dry and hot material is centrifugally cast against a revolving electrode whereby its particles of comparative elec trical conductivity become electrically charged and are thrust into one zone of an electrostatic field of force between said revolving electrode and another electrode and to a second zone of said field of force where they are momentarily sustained more or less free of the force of gravity as they centrifugally travel through said second field of force to a point of discharge, while particles of insufiicient electrical conductivity by arrest of centrifugal travel and by the force of gravity find another point of discharge substantially as described.

4. Process for electrostatic separation of finely diviided discrete material wherein thoroughly dry and hot material is centrifugally cast against a revolving electrode whereby its particles of comparative elec-' trical conductivity become electrically charged and are thrust into one zone of an electrostatic field of force between said revolving electrode and another electrode and to a second zone of said field of force where they are elevated and or sustained more or less tree of the force of gravity as they centrifugally travel through said second field of force to a point of discharge, while particles of insufficient electrical conductivity by arrest of centrifugal travel and by the force of gravity find another point of discharge, substantially as described.

5. Apparatus for electrostatic separation of finely divided discrete material comprising in combination a centrifugal pan adapted to receive said material, a charged electrode located at the outer edge of said pan, the position of said electrode being such that the material as itleaves the pan is brought into contact therewith, a second charged electrode positioned adjacent the first and forming therewith an electrostatic field of force through which the material passes after discharge from the pan, and mechanism for revolving said pan, substantially as described.

6. Apparatus for electrostatic separation of finely divided discrete material com-- prising in combination a centrifugal pan adapted to receive said material, a pair of charged electrodes forming an electrostatic field of force through which the material passes when discharged from said pan, one of said electrodes being the rim of the pan and the other a ring positioned adjacent said rim, and mechanism for revolving said pan, substantially as described,

7. Apparatus for electrostatic separation "of finely divided discrete material compasses when discharged from said pan, one i of said electrodes being the rim of the pan, a revolving ring mounted adjacent said rim and constituting the second electrode, and mechanism for revolving said pan, substantially as described.

8. Apparatus for electrostatic separation of finely divided discrete material compris-' ing in combination a centrifugal .pan adapted to receive said material, a charged electrode located at the outer edge of said pan, the position of said electrode being such that the material as it leaves the pan is brought into contact therewith, a second charged electrode mounted adjacent the first and forming therewith an electrostatic field of force through which the material passes after discharge from the pan, mechanism' for revolving said pan, and'a dividmg disc or plate outwardly of said pan, substantially as described. i v

9. Apparatus for electrostatic separation of finely divided discrete material comprising in combination a centrifugal pan adapted to receive said material, a charged electrode located at the outer edge of said pan,

the position of said electrode being such that the material as it leaves the pan is brought into contact therewith, a second 7 charged electrode mounted adjacent the first and forming therewith anelectrostatic field of force through whichthe material passes after discharge from the pan, mechanism for revolving said pan, a, dividing disc or,

plate outwardly ofsaid pan, and receiving channels "or hoppers disposed respectively inwardl and outwardly of said dividing disc, su stantially as and for thepurposesset forth. Y

10. Apparatus for'electrostatic separation of finely divided discrete materialcomprising'in combination a centrifugal panadapted to receive said material, a pair of charged an electrostatic field of electrodes formin force through'w ich the material; passes ing in combination a centrifugal pan having when discharged from said pan, one of said electrodes being the rim of the pan and the other a ring positioned adjacent said rim,-

mechanism for revolving said pan, a hopper established below said pan, the rim ofsaid hopper being outwardly of and continued above the rim of the pan, and means for discharging material from said hopper, substantially as described. 7

11. Apparatus for electrostatic separation of finely divided discrete material comprisheating elements beneath the floor thereof and adapted to, receive said material, a charged electrode located at the outer edge of said pan, the/disposal of said electrode beingsuch that the material as it leaves the pan is brought into contact therewith, a second charged electrode mounted adjacent the first and forming therewith an electrostatic field of force through which the material passes after discharge from thepan, and mechanism for revolving said pan, substantially as described.

12. Apparatus for electrostatic separation of finely divided discrete material comprising in combination a feeding hopper, a centrifugal pan, a hollow stem supporting said claiming clause, the combination with the centrifugal pan, of heating elements beneath its floor for the purposes set forth,

substantially as described andexplained'.

f 14.. In apparatus for electrostatic separation of finely divided discrete material sub-- staiiti'ally as set forth inthe preceding eighth claiming clause, the combination with the centrifugal panfand the two electrodes, of a dividin disc positionedoutwardly of said electro es, and receiving channels or hoppers, inwardlyand outwardly of said disc, substantially as and for the purposes set forth.

as and for the purposes A v p '15. ,In apparatus for electrostatic separation of finely divided discrete material, the

combination with a'frame, of a casing supportedthereby and having airports/in the top, a centrifugal pan in the casing adapted toreceive said material, mechanism fdrrecrating with said revolving'pan to remove from the latter portions of the contained material, a discharge duct c ommunicating with the'pan and a suction duct communicating with the discharge duct.

volving said pan, electrostatiemeans coopv16. Apparatus for electrostatic separation of finely divided discrete material comprisin incombination a feeding hopper, a centrifugallpan, a hollow stem supporting said pan and revolving in'the machine' frame, said stem having distributing ports to said pan, a pair of electrodes, one of said electrodes being the rim of said pana'nd-the other positioned above it, a dividing disc, two sets of receivingchannels or hoppers positioned respective y inwardly and Outwardly of said revolving dividing disc, and a by-pass valve in said hollow'stem permitting discharge from said stem direct to said inner hopper, substantially as and for the purposes set forth.

17. In and for apparatus for electrostatic separation of finely divided discrete material, the combination with a centrifugal pan, of a hollow stem supporting said pan and having a distributing chamber at the lower end thereof, said chamber having ports communicating with said pan, a valve in the floor of said chamber, and mechanism for operating said valve, substantially as and for the purposes set forth.

18. In and for apparatus for electrostatic separation of finely divided discrete material, the combination with pan 3, of a hollow stem 4, a distributing chamber 5, ports 6, I

extension ring 40, spider piece 42, wall 43, flanged piece 44, drop valve 48, plunger 47, and solenoid coil 46, substantially as and for the purposes set forth.

19. Apparatus for electrostatic separation of finely divided discrete material comprising in combination a centrifugal pan adapted to receive said material, a pair of charged electrodes forming an electrostatic field of force through which the material passes when discharged from said pan, one of said electrodes being the rim of the pan and the other a ring positioned above the rim, mechanism for revolving said pan, a dividing disc outwardly of and above the rim of said pan, and a guard ring positioned above the said ring electrode, substantially as and for the purposes set forth.

20. Apparatus for electrostatic separation of finely divided discrete material comprising in combination a centrifugal pan adapted to receive said material, a pair of charged electrodes forming an electrostatic field of force through which the material passes when discharged from said pan, one of said electrodes being the rim of the pan and the other a ring positioned adjacent saidv rim, mechanism for revolving said pan, a rotary hopper below said pan, the rim of the hopper being outwardly of'and above the rim of the pan, a discharge port in the base of said hopper, vanes in the door of the hopper for guiding material, to said discharge port, and mechanism for revolving said hopper, substantially as and for the purposes set forth.

21. In and for apparatus for electrostatic separation of finely divided discrete material, the combination with a centrifugal pan adapted to receive said material, of a charged electrode'located at the outer edge of said pan, the position of said electrode being such that the material as it leaves the pan is brought into contact therewith, a second charged electrode mounted adjacent thefirst and forming therewith an electrostatic field of force through which the material passes after discharge from the pan, mechanism for revolving said pan, a hopper located below said pan, the rim of the hopper being outwardly of and above the rim of the pan, and transformer coils and sparking needles located above the floor of said hopper, substantially as and for the purposes set forth.

22. In apparatus for electrostatic separation of finely divided discrete material, the combination with framing having a depending boss, of a toed and heeled liner mounted in the boss, a hollow stem supported by the liner, ball bearings interposed between the liner and the stem, and a pan secured to said stem, substantially as and for the purpose set forth.

23. In apparatus for electrostatic separation of finely divided discrete material, the combination with a hopper, of a hollow stem disposed below and adapted to receive material from said hopper, said stem having ports in the side thereof, a pan secured to said hollow stem and adapted to receive material passing through said ports, a flanged ring mounted on said stem, and a lateral extension on said ring constituting a hood for said pan, substantially as and for the purpose set forth.

24. In apparatus for electrostatic separation of finely divided discrete material, the combination with a pan having slots through the base thereof, of heating elements established in said slots, an annular plate covering said slots and constituting the floor of the pan, and cover elements secured to the bottom of said pan and closing the said slots at the bottom.

I 25 lln apparatus for electrostatic separation of finely divided discrete material, the combination with the pan 3, of the hollow stem 4, distributing chamber 5, ports 6, extension ring 40, spider piece 42. wall 43, flanged piece 44, drop valve 48, plunger 47, and solenoid coil 46, substantially as and for the purpose set forth.

26. In apparatus for the electrostatic separation of finely divided discrete material, the combination with a rotatable structure, of apan mounted on said structure, a set of insulated arms extending radially from said structure, a ring supported by said arms above the rim of said pan, and means for electrically charging said ring.

27. ln apparatus for electrostatic separation of finely divided discrete material, the combination with a pan, of a substantially conical hopper disposed beneath the said pan and adaptedto receive material projected from the latter, means for rotating said hopper, vanes in the fioor of said hopper adapted to direct material towards the bottom, a discharge duct extending from the center of the base of said hopper, and a suction pipe communicating with said duct 28. In apparatus for electrostatic separation of finely divided discrete material, the combination With a pan, of a hop-per disposed beneath the pan and adapted to receive material projected from the latter, and means mounted beneath the pan and above the floor of said hopper for creating an electric spark, substantially as and for the 10 purpose set forth. p

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

1 GEORGE RUD'STON BROWN; Witnesses:

FRED WALSH, CHARLES D BURNES. 

